1. Field of the Invention
The present invention relates to a new anti-adhesive composite polyester films as temporary support bases for the manufacture of polymer films, and in particular, for the manufacture of least one polyurethane layer possessing excellent optical quality and suitable for use in safety windows.
2. Discussion of the Background
It is known that plastic sheets or films meeting specific physical property requirements (in particular, resistance to scratches, transparency, surface condition, capacity for self-healing of scratches, resistance to tearing) are used for the manufacture of laminated windows, called "asymmetrical" windows, which comprise a monolithic or laminated support base made of glass and/or plastic, and said plastic sheet. These windows can be used in buildings, motorized vehicles, safety lenses, etc. Thus, French Patents 2 187 719 and 2 251 608, and European Patent 0 132 198, for example, propose placing over the glass sheet intended to be positioned to the inside of the vehicle passenger area, an elastic cross-linked polyurethane layer, termed a thermo-hardenable polyurethane layer or layer possessing surface properties, which has excellent anti-tear and self-healing properties or which can cause accidental scratches to be removed. The polyurethane layer can be used by itself or in association with another layer having adhesive and/or energy-absorbing properties, especially a thermoplastic polyurethane layer or a polyurethane layer obtained by means of reactive pouring or spraying of a mixture of reactive compounds, as described in the above-mentioned European Patent Publication No. 0 132 198.
These polyurethane layers must be of high optical quality and, in particular, must possess no surface defects. High optical quality signifies, according to the invention, the optical quality required to use these layers in the windows of transportation vehicles.
Proposals have already been offered suggesting the manufacture of these layers by pouring the liquid mass containing polyurethane precursors on a flexible, stretched plastic support base which is fed from rollers as the pouring takes place. When the thermo-hardenable polyurethane layer is formed, it can be immediately detached from the temporary plastic support base or may preferably be wound together with said support, which then acts as a protective film until its final use.
When the polyurethane film comprises a thermo-hardenable layer and a layer possessing adhesive and/or energy-absorbing properties (designated hereinafter as the EA layer), the precursors of these layers are poured successively in any order whatever, so that the temporary support base can come into contact either with the EA layer or with the thermo-hardenable layer.
The plastic material forming the temporary support base must meet various requirements as regards its surface state, its chemical inertness with respect to the polyurethane precursors, its elasticity, its capacity to be wound, and its capacity to be easily detached from the polyurethane sheet when traction is exerted on it, all the while preserving a high degree of adhesiveness in the absence of traction. The polyester films which meet a number of these requirements have been proposed as temporary support bases for polyurethane sheets, whether composite or not, for example in French Patent Publications 2 480 669 and 2 546 810. However, the polyurethane films do not achieve a desirable compromise between sufficient adherence to the polyurethane film and the capacity for easy detachment when traction is applied to the support film. The Applicants have thus set for itself the objective of using a new composite polyester film as a temporary support base for polyurethane films which can be easily detached when traction is exerted, without damaging the surface of the polyurethane film, i.e., without tearing away this surface and/or without depositing on this surface material torn away from the temporary support film.